Liquid crystalline compounds

ABSTRACT

Novel liquid crystalline compounds having a cholesteric mesophase are disclosed. The compounds have a relatively low cholesteric mesomorphic temperature range, are typically righthanded and have relatively small effective pitch. Methods of preparing the compounds and uses thereof are also described.

United Sta: 1 A

Leder June 10, 1975 LIQUID CRYSTALLINE COMPOUNDS 3,657,538 4/1972Fergason et a1. 250/83 3,697,297 10/1972 Churchill 106/]31 [75]Inventor: Lewis B. Leder, Rochester, NY.

OTHER PUBLICATIONS 73A :X c t',Stfd, 1 Sslgnee em ("mum am or Merck1ndex-8thEd.(1968),p.410.

Conn.

[ Filed: 1972 Primary Examiner-Henry A. French [21] AppL NW 300 050Attorney, Agent, or Firm-James J. Ralabate; David C.

Petre; Gaetano D. Maccarone [52] US. Cl 260/397.2; 350/160 LC 57ABSTRACT [51] Int. Cl C07c 169/58; C07c 169/60 1 [58] Field of Search260/3972 Novel hquld crystanme Compounds havmg a choles' teric mesophaseare disclosed. The compounds have a [56] References Cited relatively lowcholesteric mesomorphic temperature range, are typically right-handedand have relatively UNITED STATES PATENTS small effective pitch. Methodsof preparing the com- 2,854,452 9/1958 Lauback 260/239.55 pounds anduses thereof are also described 3,409,404 11/1968 Fcrgason....

3,580,865 5/1971 Goldberg 252/408 4 Claims, 2 Drawing Figures 1 LIQUIDCRYSTALLINE COMPOUNDS BACKGROUND OF THE INVENTION This invention relatesgenerally to liquid crystalline compounds and more specifically toliquid crystalline compounds having a cholesteric mesophase.Additionally the invention relates to uses of the novel compounds.

Recently there has been substantial interest in the discovery of moreuseful applications for the class of substances known as liquidcrystals. The name liquid crystals has become generic to liquidcrystalline materials which exhibit dual physical characteristics, someof which are typically associated with liquids and others which aretypically unique to solids. Liquid crystals exhibit mechanicalcharacteristics, such as viscosities, which are ordinarily associatedwith liquids. The optical scattering and transmission characteristics ofliquid crystals are similar to those characteristics ordinarily uniqueto solids. In liquids or fluids, the molecules are typically randomlydistributed and oriented throughout the mass of the substance.Conversely, in crystalline solids the molecules are generally rigidlyoriented and arranged in a specific crystalline structure. Liquidcrystals resemble solid crystals in that the molecules of the liquidcrystalline substances are regularly oriented in a fashion analogous tobut less extensive than the molecular orientation and structure in acrystalline solid. Many substances have been found to exhibit liquidcrystalline characteristics in a relatively narrow temperature range;but below such temperature ranges the substances typically appear ascrystalline solids and above such temperature ranges they typicallyappear as isotropic liquids.

Liquid crystals are known to appear in three different forms: thesmectic, nematic and cholesteric forms. These structural forms aresometimes referred to as mesophases thereby indicating that they arestates of matter intermediate between the liquid and crystalline states.The three mesophase forms of liquid crystals mentioned above arecharacterized by different physical structures wherein the molecules arearranged in a manner which is unique to each of the three mesomorphicstructures. Each of these three structures is well known in the liquidcrystal art.

Some liquid crystalline substances possess optically negativecharacteristics. Birefringence, also referred to as double refraction,is an optical phenomenon characteristic of some solid crystals and mostliquid crystal substances. When a beam of unpolarized light strikes abirefringent substance it is split into two polarized components whosetransverse vibrations are at right angles to each other. The twocomponents are transmitted at different velocities through the substanceand emerge as beams of polarized light. By the term liquid crystallinesubstances which have optically negative characteristics," as usedherein, is meant those for which the extraordinary index of refractionm; is smaller than the ordinary index of refraction m. Cholestericliquid crystal substances exhibit this property. For a detaileddescription of this phenomenon see Optical Crystallography, Wahlstrom,4th Edition, Wiley and Sons, lnc., New York.

The molecules in cholesteric liquid crystals are arranged in very thinlayers with the long axes of the molecules parallel to each other and tothe plane of the layers within each layer. Because of the structuralasymmetry and steric nature of the molecules the direction of the longaxes of the molecules in each layer is displaced slightly from thecorresponding direction in adjacent layers. This displacement iscumulative over successive layers so that overall displacement tracesout a helical path. A comprehensive description of the structure ofcholesteric liquid crystals is given in Molecular Structure and theProperties of Liquid Crystals, G. Wv Gray, Academic Press 1962.

Cholesteric liquid crystals have the property that when the propagationdirection of plane polarized or unpolarized light is along the helicalaxis thereof, i.e., when the light enters in a direction perpendicularto the long axes of the molecules, (neglecting absorptionconsiderations), this light is essentially unaffected in transmissionthrough thin films of such liquid crystals except for a wavelength bandcentered about some wavelength A where A 2np with n representing theindex of refraction of the liquid crystal substance and p the pitch orrepetition distance of the helical structure. The bandwidth of thiswavelength band centered about X will typically be of the order of aboutA,,/l4. For light ofa wavelength A the cholesteric liquid crystal, underthese conditions, exhibits selective reflection of the light such thatapproximately 50 percent of the light is reflected and approximately 50percent is transmitted, assuming negligible absorption which is usuallythe case, with both the reflected and transmitted beams beingapproximately circularly polarized in opposite directions, respectively.

For light having wavelengths around A but not at )t the same effect ispresent but not as pronounced. The transmitted light is not circularlypolarized but is instead elliptically polarized. The cholesteric liquidcrystals which exhibit this property of selective reflection of light ina region centered around some wavelength )t are said to be in theGrandjean or disturbed texture. lf A, is in the visible region of thespectrum the liquid crystalline film appears to have the colorcorresponding to A and if A, is outside the visible spectral region thefilm appears colorless.

Depending upon the intrinsic screw sense of the helix, i.e., whether itis right-handed or left-handed, the light that is transmitted in theregion about a is either right-hand circularly polarized light (RHCPL)or lefthand circularly polarized light (LHCPL). The transmitted light iscircularly polarized with the same sense as that intrinsic to the helix.Thus, a cholesteric liquid crystal having an intrinsic helical structurewhich is left-handed in sense will transmit LHCPL and one having ahelical structure which is right-handed in sense will transmit RHCPL.

Hereinafter these cholesteric liquid crystal substances will beidentified in order to conform with popular convention, by the kind oflight which is reflected at )thd 0. When a film is said to beright-handed, it is meant that it reflects RHCPL, and when a film issaid to be left-handed, it is meant that it reflects LHCPL.

A right-handed cholesteric liquid crystal substance transmits LHCPLessentially completely at A, whereas the same substance reflects almostcompletely RHCPL. Conversely a left-handed film is almost transparent toRHCPL at A and reflects LHCPL. Since plane polarized or unpolarizedlight contain equal amounts of RHCPL and LHCPL, a cholesteric liquidcrystal film is approximately 50 percent transmitting at )t for thesesources when the liquid crystal is in its Grandjean texture.

A further unique optical property of optically negative liquid crystalfilms is that contrary to the normal situation when light is reflected,such as by a mirror, where the sense of the circular polarization of thereflected light is reversed, this same phenomenon does not occur withlight reflected by these liquid crystal films. The sense of the circularpolarization of light reflected from these liquid crystal substances isnot reversed but rather remains the same as it was before it came intocontact with the liquid crystal substance. For example, if RHCPL havinga wavelength )t is directed at a right-hand film having A 2np it issubstantially completely reflected and, after reflection, remains RHCPL.If the same light were to be directed on a mirror the reflected lightwould be LHCPL.

Because of these optical properties, optically negative liquidcrystalline substances have been found to be highly advantageous for usein a number of varying applications. US. Pat. Nos. 3,669,525 and3,679,290 disclose the use of such liquid crystalline materials inoptical filter systems. The materials may be advantageously utilized inimaging methods such as are disclosed in US. Pat. Nos. 3,642,348 and3,652,148. The thermal properties of these materials make themadvantageous for use in thermometers, in detecting flaws in structuralmembers and in medical applications. Of course many other uses could bedescribed but these should be sufficient to indicate the varied andimportant applications of optically negative liquid crystals.

In many of the applications cited above it would be desirable to have aliquid crystalline material which exists in the cholesteric mesophase atsome temperature around room temperature (about 23C); although there arealso applications where it is to be desired to have the liquidcrystalline material in this optically active state above roomtemperature or below room temperature. To achieve a material having aparticular desired operational cholesteric mesomorphic temperature aswell as other desired properties, e.g., a particular pitch or electricfield sensitivity, it has heretofore been the usual practice to formcompositions which are made up entirely of cholesteric liquid crystalsor combinations of cholesterics and nematic liquid crystals orcombinations of cholesterics and smectic liquid crystals.

Furthermore it has been found that considerable versatility can beachieved with respect to cholesteric liquid crystals by mixing togethercombinations of righthanded and left-handed cholesteric liquid crystals.In such a mixture there is a composition at which the right-handed andleft-handed components nullify each other to provide an infinite pitch.This technique also makes it possible to generally achieve a broaderrange of pitches than typically can be achieved by mixing together onl',right-handed or only left-handed materials. See Proc. ACS Symposium onOrdered Fluids and Liquid Crystals, Sept. 1969, p. 463.

Many left-handed cholesteric liquid crystalline materials are known;however to date only relatively few right-handed materials have beenprovided. Moreover a difficulty with respect to potential uses ofcholesteric liquid crystalline materials in electro-optic devices hasbeen the relatively high temperatures at which the majority of the knowncholesteric materials become mesomorphic. Typically, electro-opticdevices are operated at or near room temperature. Thus devices utilizingcholesteric liquid crystals having relatively high mesomorphictemperature ranges would require additional apparatus to maintain thetemperature of the liquid crystalline materials within their mesomorphicrange thereby undesirably complicating the overall device configuration.Therefore there exists a continuing need for cholesteric liquidcrystalline materials which have mesomorphic temperature ranges at ornear room temperature and particularly so for such materials which areright-handed.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide novel liquid crystalline materials which have a cholestericmesophase and possess the above-described desirable features.

It is another object to provide liquid crystalline materials having acholesteric mesophase at or near room temperature.

It is a further object to provide liquid crystalline materials whichhave a relatively small effective pitch.

A further object is to provide liquid crystalline materials which have aright-handed cholesteric mesophase.

It is still another object to provide methods for preparing such novelliquid crystalline materials.

Yet another object is to provide liquid crystalline materials which areuseful in electro-optical applications.

A still further object of the invention is to provide such liquidcrystalline materials which may be utilized in electro-optic imaging anddisplay devices.

The foregoing and other objects and advantages are accomplished inaccordance with the invention by providing novel liquid crystallinecompounds which are represented by the general formula H CH 817 where Ris a radical which may be a carbonate, ester, ether, thiocarbonate,thioester, thioether, xanthate or halide.

The novel compounds of the invention are typically right-handedcholesteric liquid crystalline materials, have a relatively smalleffective pitch and are advantageous for use in many applicationsincluding various electro-optic imaging techniques which will bedescribed in detail further below.

The invention will be more fully understood from the following detaileddescription of various embodiments thereof particularly when read inconjunction with the accompanying drawings wherein:

FIG. 1 is a plot of l/ vs the 3B addition for various cholesteryl anddoristeryl derivatives; and

FIG. 2 is a plot of l/A for various cholesteric liquid crystallinematerials.

The novel compounds of the invention are derivatives of a steroidcompound having the formula HO- it which will, for simplicity, bereferred to hereinafter as doristerol although it should be recognizedthat this steroid has been identified in various instances in the art asA8(l4)-cholestanol or cholest-8(l4)-en-3B-ol. Hereinafter the compoundsof the invention will be referred to as doristeryl compounds.

it will be apparent that doristerol is structurally similar tocholesterol which is represented by the formula CH3 CH3 j A detaileddescription of the preparation of doristerol will be provided belowherein.

The doristeryl derivatives which are the novel compounds of theinvention can be synthesized by various techniques. According to onemethod the 7- dehydrocholesteryl compound is formed by reacting7-dehydrocholesterol with the appropriate alkyl chloroformate to formcarbonates or with the appropriate alkyl acid anhydride to form esters.These are subsequently hydrogenated with an appropriate catalyst toprovide the desired doristeryl compound. Another technique compriseshydrogenating 7- dehydrocholesterol to form doristerol and then reactingthe doristerol with appropriate compounds such as, for example, alkylchloroformates to form doristeryl carbonates or alkyl acid anhydrides toform doristeryl esters. This latter technique is preferred since it hasbeen found through experimentation that higher yields are typicallyobtained.

Of course other methods for forming the advantageous compounds of theinvention will be apparent to those skilled in the art. For example, thedoristeryl carbonates can be made by first preparing the doristeryl or7-dehydrocholesteryl chloroformate and then reacting either of thesecompounds with the appropriate alkyl alcohol. In preparing the esters ofdoristerol, where the alkyl acid anhydride is not easily available, thedoristeryl ester can be made in the manner described by Elser,

Pohlmann and Boyd, Molec. Crystals and Liquid Crystals, l l, 279 (1970)for the preparation of cholesteryl alkanethioates by reacting doristerolwith the imidazolide of the alkanoic acid.

There are known reaction sequences which can be employed to substitute Sfor O in esters, carbonates and ethers of doristerol. For example the-OH attached to the ring system in doristerol can be converted to Sl-l.This latter compound can be converted to a thiocarbonate by the samereaction sequences employed to make carbonates of doristerol. Reactionsof the O anion of doristerol with carbon disulfide followed byalkylation with an alkyl halide will provide the xanthate derivatives ofdoristerol.

The novel compounds of the invention typically have relatively lowmesomorphic temperature ranges and, further, these are typicallysignificantly lower than those of the corresponding cholesterylcompounds. In Table I there are shown the critical temperatures for thechloride and some esters and carbonates of doristerol. All of thesematerials are cholesteric; the chloride, butyrate, pentanoate, hexanoateand heptanoate are monotropic while the others are enantiotropic.

All of the doristeryl and cholesteryl compounds listed in Table l whichare not referenced were measured by differential scanning calorimetry(DSC) or by the capillary method wherein the material is placed in acapillary tube which is immersed in an oil, the oil heated and meltingobserved with a magnifying glass and the temperature taken from athermometer immersed in the oil. For a more detailed description of thelatter technique see Molecular Structure and the Properties of LiquidCrystals, G. W. Gray, Academic Press (1962) RD. Ennulat. Molec. Cryst. &Liquid Cryst. 8. 247 W69) "W. Elsur. Molec. Cryst. 2, l (1966) "G. W.Gray. J. Chem. 500., 3733 (I956) R. D. Ennulat, Molec. Cryst 3. 405(I968) As previously mentioned, the novel compounds of the inventiontypically have a relatively small effective pitch. In Table 11 there areshown the )t (pitch) values for some of the compounds.

TABLE II Doristeryl Compound A,,(;L)

PROPIONATE 0.13 3 BUTYRATE 0.141 PENTANOATE 0.153 HEXANOATE 0.158HEPTANOATE 0.175 OCTANOATE 0.200 NONANOATE 0.230 HEXYL CARBONATE 0.143HEPTYL CARBONATE 0.143 OCTYL CARBONATE 0.159

The pitch values were determined by making mixtures of varyingproportions of each compound with cholesteryl oleyl carbonate. Thecritical wavelength, A for each composition was measured with a Cary 14Spectrophotometer. The incident light was unpolarized and normal to thesample plane and transmission spectra were recorded. A plot of l/lt vs.wt. percent of doristeryl compound was then extrapolated to 100 percentto obtain the effective pitch and rotatory sense. A detailed descriptionof this method can be found in Chem. Phys. Letters, J. E. Adams and L.B. Leder, 6, 90 (1970); and J. Chem. Phys., L. B. Leder, 54, 4671(1971).

As stated above, the novel liquid crystalline compounds are typicallyright-handed materials. Following is a proposed theoretical explanationfor this typical property of the doristeryl derivatives to better aidthose skilled in the art to understand the invention. It should berecognized of course that the invention is not intended to be limited bythese theoretical considerations. Nevertheless observed experimentalresults are consistent with the proposed theory. Applicant haspreviously shown that structural changes in the 17 side chain ofcholesterol as well as the effective length of the 3B addition candetermine the magnitude of pitch for a cholesteric liquid crystallinematerial. See J. Chem Phys. 54, 4671 (1971) and J. Chem. Phys. 155, 2649(1971 In the former article it was disclosed that the cholesterolskeleton is basically right-handed and that additions at the 3B positionhave a tendency to decrease the right-handedness (or increase the pitch)until at some critical length of the 3B additive, in that case about2.08A, the cholesteryl compounds become left-handed. In the same mannerit has been shown that the doristeryl skeleton is also right-handed butmore so than the cholesterol skeleton" and that additions at the 33position also have the tendency to decrease the right-handedness up tosome critical length. In the case of the doristeryl compounds thecritical length is about 2.81A. For a graphical illustration of theforegoing see FlG. 1.

Now it is theorized that a third factor which operates to determine thehandedness, or chiral sense, of a steroidal cholesteric liquidcrystalline compound is the position (or positions) of the doublebond(s) in the steroid ring system. The doristeryl compounds have adouble bond in the 8-14 carbon position and it appears that this doublebond position is particularly effective in orienting the ring system insuch a direction as to make the resultant compounds typically stronglyrighthanded.

This phenomenon is graphically illustrated in FIG. 2. Referring now toFIG. 2 there is seen a plot of ll) for the sterols and the sterylchlorides, acetates, and benzoates for several double bondconfigurations. The horizontal axis is arranged in the order ofincreasing righthandedness of the sterol skeleton as one goes from leftto right on the figure. The cholestanol skeleton, which is representedby the formula is chosen as a reference point since it does not have anydouble bond in the ring system. It can be readily seen that the additionof the 56 double bond in cholesterol tends to reduce theright-handedness of the compounds whereas the addition of the doublebond in the 8l4 position for doristerol tends to increase it. Forexample, 1/)\,, for cholesteryl chloride is approximately 2/3 that forcholestanyl chloride while for doristeryl chloride is approximately 4.3times that for cholestanyl chloride. When a second double bond is addedat the 7-8 carbon position thus forming 7-dehydrocholesterol a furtherdecrease in l/l occurs so that this value for the chloride of7-dehydrocholesterol is about one-third that for cholestanyl chlorideand approximately one-half that for cholesteryl chloride.

The novel compounds of the invention can be advantageously utilized inany method, device, etc. wherein cholesteric liquid crystallinematerials are used. Typical applications in which the compounds may beused include, for example: optical filters such as are disclosed in U.S.Pat. Nos. 3,669,525 and 3,679,290 and copending application Ser. No.121,378, filed Mar. 5, 1971 now U.S. Pat. No. 3,71 1,181; electro-opticapplications such as, for example, the imaging techniques disclosed inU.S. Pat. Nos. 3,642,348 and 3,652,148; displays, detection devices suchas thermal, pressure vapor sensitive devices and many others.

The invention will now be further described in detail with respect tospecific preferred embodiments thereof by way of Examples, it beingunderstood that these are intended to be illustrative only and theinvention is not limited to the materials, percentages, conditions,etc., which are recited therein. All parts and percentages recited areby weight unless otherwise specified. IR spectra confirm the presence ofthe compound expected from the reaction described in each example.

EXAMPLES All of the doristerol compound used in the examples is made bythe following procedure: 7-

dehydrocholesterol (available commercially from Aldrich Chemical Co.) ispurified by recrystallization from acetone by first dissolving aquantity of the compound in hot acetone and then allowing the acetone tocool slowly so that the dissolved 7-dehydrocholesterol comes out ofsolution in pure form. The 7-dehydrocholesterol is then hydrogenated.For hydrogenation about 2 grams of 7-dehydrocholesterol is dissolved ina mixture of 285 ml ethyl acetate and 15 ml acetic acid to which isadded about 0.25 gm. of 10 percent palladium on carbon catalyst. Thisreaction mixture, contained in a suitable glass vessel, is pressurizedwith several atmospheres of 9. hydrogen (about 50 lbs.) and shaken in anappropriate apparatus for about 19 hours.

After the hydrogenation process is completed the palladium on carboncatalyst is filtered off from the solution. The liquid portions areremoved by standard procedures and the solid doristerol is purified byrecrystallization from methyl alcohol or other suitable solvent. Forhighest purity column chromatography techniques may be used.

Of course, it will be understood that the proportions shown above aretypical and they may be varied within some limits. For example, theamount of catalyst or acetic acid may be increased or the reaction timeshortened. The amount of ethyl acetate used is generally governed by theamount of 7-dehydrocholesterol used because of solubility factors.Chloroform may be employed as a solvent rather than ethyl acetate. Thechl roforrn has the advantage of being able to dissolve more7-dehydrocholesterol and thus more of the latter can be hydrogenated ina given reaction.

EXAMPLE I About 2.5 grams of doristerol and about 1.07 grams of hexylchloroformate are dissolved in about 50 ml of dry benzene in athree-necked flask which is equipped with a dropping funnel and acondensation column. In the dropping funnel is placed a solution ofabout 1 ml of dry pyridine in about 20 ml of dry benzene. Dry nitrogenis passed through the flask while the reaction mixture is stirred andthe dry pyridine-benzene solution is allowed to slowly drop into thereaction mixture. After the pyridine-benzene solution is added, theentire reaction mixture is heated to reflux with stirring and refluxingcontinued until the reaction is completed (about 4 hours).

The solution is then cooled to room temperature and the solid doristerylhexyl carbonate recovered by filtration and flash evaporation. Thecompound is redissolved in anhydrous ether. washed with both acid andbasic water solutions, dried, flash evaporated and finally purified byrecrystallization from methyl alcohol.

It will be understood that proportions other than those listed may beused in this procedure except that the alkyl chloroformate should be atleast equimolar with the steryl alcohol.

EXAMPLE II Doristeryl heptyl carbonate is made by the proceduredescribed in Example I with the exception that about 3 grams ofdoristerol and about 1.39 grams of heptyl chloroformate are initiallydissolved in 30 ml of dry benzene.

EXAMPLE III About 5 grams of 7-dehydrocholesterol and about 2.13 gramsof hexyl chloroformate are dissolved in about 187 ml of dry benzene in athree-necked flask which is equipped with a dropping funnel and a condensation column. In the dropping funnel is placed a solution of about lml of dry pyridine in about m1 of dry benzene. Dry nitrogen is passedthrough the flask while the reaction mixture is stirred and the drypyridine-benzene solution is allowed to slowly drop into the reactionmixture. After the pyridine-benzene solution is added, the entirereaction mixture is heated to reflux with stirring and refluxingcontinued until the reaction is completed (about 4 hours). The 7dehydrocholesteryl hexyl carbonate formed in this manner is recovered bythe same techniques described in Example I.

About 0.75 gram of 7-dehydrocholesteryl hexyl carbonate is dissolved ina mixture of 255 ml ethyl acetate and 15 ml acetic acid to which isadded about 0.25 gram of 10 percent palladium on carbon catalyst. Thisreaction mixture, contained in a suitable glass vessel, is pressurizedwith several atmospheres of hydrogen (about 50 lbs.) and shaken in anappropriate apparatus until hydrogenation is complete. The doristerylhexyl carbonate is recovered and purified by the same techniquesdescribed in Example I.

EXAMPLE IV Doristeryl heptyl carbonate is made by the same proceduredescribed in Example III. 7-dehydrocholesteryl heptyl carbonate is madeusing about 10 grams of 7- dehydrocholesterol and about 4.7 grams ofheptyl chloroformate dissolved in about 400 ml benzene to which wasadded 4 ml of pyridine. I

About 0.51 gram of 7-dehydrocholesteryl heptyl carbonate is dissolved ina mixture of 40 ml ethyl acetate and 6 ml acetic acid to which is addedabout 0.2 gram of 10 percent palladium on carbon catalyst. Doristerylheptyl carbonate is formed as a result of hydrogenation.

EXAMPLE V Doristeryl octyl carbonate is made by the same proceduredescribed in Example III. 7-dehydrocholesteryl octyl carbonate is madeusing about ,5 grams of 7- dehydrocholesterol and about 2.5 grams ofoctyl chloroformate dissolved in about 150 ml of benzene.

About 0.6 gram of 7-dehydrocholesteryl octyl carbonate is dissolved in amixture of about 50 ml ethyl acetate and I0 ml acetic acid to whichabout 0.3 gram of catalyst is added. Doristeryl octyl carbonate isformedv by the hydrogenation reaction.

EXAMPLE VI About 1.9 grams of doristerol, ml of propionic anhydride and20 ml of dry pyridine are heated to-. gether in a flask through whichdry nitrogen is flowed. After about three hours the liquors are pouredover ice and the doristeryl propionate reaction product precipitated outon the ice. The precipitate is filtered from the liquids, redissolved inanhydrous ether and recovered and purified by the same techniquesdescribed above in Example I.

EXAMPLE VII Doristeryl butyrate is made by the same procedure describedin Example V1 with the exception that about 2.75 grams of butyricanhydride is used.

EXAMPLE VIII Doristeryl pentanoate is made by the same proceduredescribed in Example VI using about 2.2 grams of doristerol and about3.75 grams of pentanoic anhydride.

EXAMPLE IX Doristeryl hexanoate is made by the same procedure describedin Example VI using about 2.3 grams of doristerol and about 4.5 grams ofhexanoic anhydride.

EXAMPLE x A solution of about 0.67 gram of heptanoic acid in about 5 mlof benzene is added to a stirred slurry of about 0.81 gram of 1,1-carbonyldiimidazole in about 13 ml of benzene in a flask. The mixtureis stirred in a nitrogen atmosphere until CO evolution ceases (about 20minutes). About 1.94 grams of doristerol are then added and the entiremixture refluxed for about 6 hours. The doristeryl heptanoate formed bythis reaction procedure is recovered by the same techniques described inExample 1.

EXAMPLE XI Doristeryl octanoate is made by the procedure described inExample X using about 0.72 gram of octanoic acid.

EXAMPLE XII About 3.0 grams of doristerol and about 1.85 grams ofnonanoyl chloride in 42 ml of pyridine are placed in a flask, heated ina nitrogen atmosphere with stirring at about 100C for about 4 hours. Thesolution is then allowed to cool and stirring is continued for about 12hours. The doristeryl nonanoate formed by this reaction is recovered andpurified by the same techniques described in Example I. Doristerylnonanoate (C H O requires 82.07% C; 11.86% H; 6.07% O. The elementalanalysis for the compound prepared is 82.28% C; 12.00% H; 5.72% 0.

EXAMPLE XIII About 15 grams of cholesteryl chloride are dissolved inabout 75 ml of petroleum ether (B.P. 60110C). About 7.5 grams ofN-bromosuccimide and a few milligrams of benzoyl peroxide are added tothe solution. The mixture is refluxed for about 1% hours after which itwas flash evaporated. About 27.75 grams of diethylaniline is then addedand the mixture heated for about 3 hours at 95C. The solution is thencooled and about 75 ml of petroleum ether added. The precipitateddiethylaniline hydrobromide is filtered off and the filtrate washed withdilute HCL and sodium carbonate solutions. The ether extracts are driedover anhydrous sodium sulfate.

The ether is evaporated and the residue (a liquid) is dissolved in about15 ml of acetone and allowed to stand. The crystals of7-dehydrocholesteryl chloride which form are filtered off and thenrecrystallized from acetone and decolorising charcoal. To further purifythe material. the crystals are refluxed in pyridine for about 2 hoursand the solution then allowed to cool. Water is added slowly to inducecrystallization. The re sulting crystals are filtered off andrecrystallized from acetone.

About 1 gram of 7-dehydrocholesteryl chloride is dissolved in about 120ml ofa 5:1 mixture of ethyl acetate: acetic acid and to this is addedabout 0.3 gram of a 10 percent palladium on charcoal catalyst. Thismixture is hydrogenated for about 24 hours. The crude doristerylchloride is recovered by filtration and subsequently purified by thesame techniques described above.

EXAMPLES XIV-XVII The synthesis of the esters in these examples iscarried out via the transacylation reaction of imidazolide as describedin Angew. Chem., H. A. Staab, 71, 194

(1959). All the experiments are carried out under nitrogen.

EXAMPLE XIV A solution of 1.03 grams of decanoic acid in 20 ml of drybenzene is added to a mixture of 0.97 gram of 1,1 -carbony]diimidazo1e(available commercially from Aldrich Chem. Co., Inc., Milwaukee,Wisconsin) in 30 ml of dry benzene with stirring. When the evolution ofCO has ceased, 1.92 grams of doristerol are added. The reaction mixtureis refluxed for about 4-5 hours and benzene is distilled off. Theresidue is mixed with 100 ml of dry hexane, the precipitated imidazoleis removed by filtration and the filtrate chromatographed on a 20 X 450mm column of silica gel (Baker analyzed reagent, 60-200 mesh).

Elution with a 2:8 mixture of benzene and hexane provided 2.23 grams ofchromatographically purified doristeryl decanoate. Recrystallizationfrom acetone gave fine crystals. Doristeryl decanoate (C H O requires82.16% C; 11.93% H; 5.91% O. The elemental analysis for the compoundpreparct. is 82.10% C; 12.06% H; 5.84% 0.

EXAMPLE XV The procedure described in Example XIV is repeated with theexception that 1.20 grams of dodecanoic acid are used in place of thedecanoic acid. 2.33 grams of chromatographically purified doristeryldodecanoate are obtained. Doristeryl dodecanoate (C H O requires 82.33%C; 12.04% H; 5.63% O. The elemental analysis for the compound preparedis 82.19% C; 12.01% H; 5.80% 0.

EXAMPLE XVI The procedure described in Example XIV is repeated with theexception that 1.29 grams of tridecanoic acid are used in place of thedecanoic acid. 2.34 grams of chromatographically purified doristeryltridecanoate are obtained. Doristeryl tridecanoate (C H O requires82.41% C; 12.0l% H; 5.49% O. The elemental analysis for the compoundprepared is 82.32% C; 12.05% H; 5.63% 0.

EXAMPLE XVII The procedure described in Example XIV is repeated with theexception that 1.37 grams of tetradecanoic acid are used in place of thedecanoic acid. 2.33 grams of chromatographically pure doristeryltetradecanoate are obtained. Doristeryl tetradecanoate (C H O requires82.48% C; 12.16% H; 5.36% O. The elemental analysis for the compoundprepared is 82.33% C; 12.30% H; 5.37% 0.

Although the invention has been described in detail with respect tospecific preferred embodiments thereof, it should be understood thatthese are not intended to be exhaustive and the invention is not limitedthereto but rather it will be appreciated by those skilled in the artthat modifications and variations are possible which are within thespirit of the invention and the scope of the claims.

What is claimed is:

1. Liquid crystalline compounds having a cholesteric mesophase which arerepresented by the formula wherein R represents a member selected fromthe group consisting of halogens, aliphatic ester radicals having fromthree to fifteen carbon atoms and carboning nine carbon atoms.

1. LIQUID CRYSTALLINE COMPOUNDS HAVING A CHLOESTERIC MESOPHASE WHICH AREREPRESENTED BY THE FORMULA
 2. The compounds as defined in claim 1wherein R represents a halogen.
 3. The compounds as defined in claim 1where R represents an aliphatic ester radical having from three tofifteen carbon atoms.
 4. The compounds as defined in claim 1 wherein Rrepresents a carbonate radical having up to and including nine carbonatoms.